The purpose of this project is to synthesize a variety of organic compounds labeled with gamma-emitting nuclides and to ascertain their ability to selectively concentrate in tumors or organs. The rationale for the design of these compounds is generally based on published biochemical and/or pharmacological findings. Agents for the clinical diagnosis of uveal melanomas and adrenal cortical tumors have resulted from this project and a potentially useful myocardial scanning agent is in the final stages of pre-clinical work-up. While current research is focused on the development of diagnostic imaging agents for a variety of endocrine tumors, agents which display a potential for photoscanning other organs will not be ignored. BIBLIOGRAPHIC REFERENCES: Skinner, R. W. S., Pozderac, R. V., Counsell, R. E., and Weinhold, P.A., The Inhibitive Effects of Steroid Analogues in the Binding of Tritiated 5-alpha-Dihydrotestosterone to Rat Proteins from Rat Prostate Tissue, Steroids, 25, 189, 1975. Counsell, R. E., Ranade, V. V., Kline, R., Hong, B.H., and Buswink, A., Potential Tumor or Organ Imaging Agents. 15. Radioiodinated Diphenylhydantoin Derivatives, J. Pharm. Sci., in press.